Time period device



Nov. 17, 1931. G. M. WRIGHT 1,832,345

TIME PERIOD DEVICE Filed Oct. 21. 1929 INVENTOR GM. vmasn ATTORNEYPatented Nov. 17, 1 931 UNITED STATES PATENT OFFICE GEORGE MAURICEWEIGHT, 0]? IQADDOW, CHELMSFOBD, ENGLAND, ASSIGNOR TO RADIO CORPORATIONOF AMERICA, A CORPORATION OF DELAWARE TIME PERIOD DEVICE Applicationfiled October 21, 1929, Serial No. 401,344, and in Great Britain October22, 1928? This invention relates to time period devices, and has for itsprincipal object to.

provide a time period device which shall be substantially independent.of temperature variations.

In cases where an extremely constant alternating current frequency isrequired, e. g.,

picture telegraphy, transmitted radio wave lengths, frequency standards,etc., one method of achieving the required constancy is to employ anelectrically maintained time period device, such as a tuning fork, forthe production of the alternating current. I

At the present time such a generator can be constructed so that itsfrequency is practically independent of all disturbin factors savetemperature. In certain applications, for example, single wave lengthsworking in broadcasting, trouble is experienced in main-. taining asufliciently accurate temperature control, and consequently it isdesirable to obtain a generator which is independent of the temperatureatwhich it is operating.

According to this'invention, as shown by the single figure of thedrawing, a time period device comprises two time period elements, theratio of whose frequencies at a and its temperature coefiicient being B,the

forks are so made and are of such material that other brass, the latterbeing provided with small iron armatures on the tines in order that itmay be maintained in vibration.

With this arrangement, assuming both forks to be subjected to the sametemperature changes, if any, the'beat frequency does not vary with suchchanges. This will be seen from the following proof: I

At any temperature If above datum, the frequencies of the forks will berespectively fl (l-at) and f2 (lBt) and the beat frequency at thistemperature will be But gf Bf Hence fl flatf2+f2 I Bt=flf2= the beatfrequency at datum temperature.

Having now described my invention in one of its preferred forms, othermodifications and changes will suggest themselves. and at once becomeapparent to thoseskilled in the art to which it relates. I, therefore,believe myself to be entitled to any and all modifications fallingfairly within its spirit and scope as set forth in the hereinafterappended claims; wherein I claim:

1. A time period device comprising two time period elements the ratio ofwhose frequencies at a given temperature is substantiallyinverselyproportioned totheir temperature coefficient.

2. A time period device as claimed in claim 1 and comprising two tuningforks so arranged that ifthe frequency of one tuning fork at a giventemperature is f1 and its tomperature coefficient is a, the frequency ofthe other fork being f2 at the same temperature and its temperaturecoefiicient being B, the forks are so made and are 'of such materialthat 3. In atime period device, a plurality of tuning forks, one of saidtuning forks having a temperature coefiicient of a at a frequency f1,the other of said tuning forks having av temperature coefiicient of B ata. frequency f2 at the same temperature and a ratio of being establishedbetween the two forks, means for independently driving each of saidforks, and a combining circuit for utilizing the combined output energyfrom said forks. GEORGE MAURICE WRIGHT.

